This invention refers to an ultrasonic welding apparatus and more particularly to an apparatus for sealing plastic film bags. Quite specifically, this invention concerns an ultrasonic welding apparatus for sealing plastic film bags wherein the open end of the bags is gathered, possibly twisted, and then sealed by providing a weld. Bags of this type are used primarily for packaging irregularly shaped articles, such as meat, fresh produce, etc.
The process and apparatus for closing plastic film packages or bags of the type indicated is known in the prior art, see, for instance, U.S. Pat. No. 3,667,594 issued to A. D. Herrell, dated June 6, 1972, entitled "Closure for Film Packages and Method of Making Same", and U.S. Pat. No. 3,780,488, issued to A. D. Herrell, dated Dec. 25, 1973 entitled "Closure for Film Packages and Method of Making Same". A similar method and apparatus for ultrasonically sealing thermoplastic net bags is shown in U.S. Pat. No. 4,190,690, issued to K. Rabeneck et al, dated Feb. 26, 1980 entitled "Manufacture of Sealed-End Tubular Thermoplastic Net Bagging", and in U.S. Pat. No. 4,289,569 dated Sept. 15, 1981 issued to the same inventors.
Ultrasonic sealing of bags and netting as shown in these prior art devices have not been entirely satisfactory, thereby impeding wide-spread commercial use of this method of bag sealing.
The present invention concerns an improved arrangement and particularly reveals an improved anvil structure for the ultrasonic sealing apparatus. Specifically, this invention discloses an anvil construction in which the anvil has a recess into which the gathered bag closure material is inserted for welding. The ultrasonic resonator, or horn, is shaped to enter the recess of the anvil to provide ultrasonic energy to the gathered closure material. The specific improvement disclosed herein concerns the provision of a sliding fit between the resonator portion entering the anvil recess and the anvil recess in order to prevent the extrusion of plastic film material into the side or wall space between the resonator and the anvil. Such extrusion or escapement of film material interferes with the provision of a hermetic seal. In order to avoid the destruction of the resonator surface and the anvil surfaces, which are in sliding contact with each other, the anvil surfaces facing the resonator are lined with a low friction material.
One of the principal objects of this invention, therefore, is the provision of a new and improved ultrasonic welding apparatus.
Another and important object of this invention is the provision of an improved ultrasonic welding apparatus for providing a closure on film bag material, wherein the closure is provided by gathering the bag material and welding the gathered material to cause a welded nugget.
Another important object of this invention is the provision of an ultrasonic welding apparatus for providing a closure on thin film bag material wherein the closure end comprises gathered film material which is adapted to be confined in the recess of an anvil during the welding process.
A still further and other object of this invention is the provision of an ultrasonic welding apparatus having an anvil which exhibits a recess lined with low friction material.
Further and still other objects of this invention will become more clearly apparent by reference to the following description when taken in conjunction with the accompanying drawings.